You can't see Gaspar Noé's Irreversible without starting a heated discussion with someone else who saw it, or part of it. Many viewers walk out midway through, during the nine-minute scene in which Alex, played by the beautiful Monica Bellucci, is beaten and anally raped in the lurid red light of a Paris underpass as Noé stations his camera and watches.

It would be easy and convenient to dismiss Irreversible as blatant sensationalism. But Noé's bruising film is too artfully crafted to write off as exploitation. To see it is to absorb it, even against your will. Noé, the acclaimed French director of Carne and I Stand Alone, tells his story backward, as in Memento, but offers nothing as comforting as amnesia.

Irreversible opens with the credits running backward. A strange man (Philippe Nahon) states, "Time destroys everything." We are then thrust into a scene of revenge. Alex's lover, Marcus (Vincent Cassel), and her ex-boyfriend Pierre (Albert Dupontel) enter a gay S&M club looking for the rapist and end up — as the camera swirls among writhing bodies and hard-ons - bashing in the head of the wrong man with a fire extinguisher, a moment so brutal as to prompt walkouts even before the rape that follows.

It's the last third of the film that eases up. We watch Alex, Marcus and Pierre at a party where Alex and Pierre quarrel and she leaves, heading for the underpass. Noé then tracks further back to Alex and Marcus in bed, naked and tender with each other. Bellucci and Cassel, married in real life, give these scenes an erotic charge laced with affection and delicacy. It's this harmony that time destroys, except, of course, in Noé's film, where time is at the mercy of the filmmaker. Noé's considerable accomplishment is to examine the relationship between life and art, time and memory. Irreversible means to knock you for a loop. It does.